After unpacking, each dictionary (three files) resides in a a separate subdirectory. All these subdirectories are put into the "dicts" directory on the SD card.

There is one big warning, however.
On a PC, utilities which work with dictionaries (e.g. stardict) will automatically show all relevant entries from all available dictionaries (when you "search" for a word).
This is NOT the case on M92. The utility here, that's responsible for dictionary search, is only able to work with a single dictionary at a time. You need to switch dictionaries manually yourself -> there is a special "icon" in form of a small book, just above the keyboard (when you click that icon you should see the full list of available dictionaries).

One small note: somebody was claiming somewhere that the current firmware needs dictionaries in "stardict-2" format (e.g. "stardict-*-2.4.2"), not in the "stardict-3" format.